This invention relates to arrangements for the efficient large-scale integration of optical waveguiding circuits including thin-film type waveguiding circuits.
Rapid progress has been made in recent years in the field of integrated optics, including primarily thin-film integrated optical circuits but also the interfacing of such circuits with optical fiber waveguiding circuits and systems.
Nevertheless, the development of economical and effective integration of optical waveguiding circuits still faces many practical problems. Particularly, a thin-film laser intended for an integrated arrangement has been proposed to be made with a grating structure to be formed on the active layer. This grating structure forms the optical resonator and eliminates the need for conventional discrete mirrors that are incompatible with large scale integration of optical circuits.
Nevertheless, the grating-forming process introduces a high resistance region or surface which drastically degrades the efficiency of the laser.
The next problem is that it is typically desirable to form active optical devices on a semiconductor substrate, usually gallium arsenide or gallium aluminum arsenide, which has a relatively large refractive index. On the other hand, the passive part of the integrated optical circuit typically needs a relatively low refractive index, and, preferably, an amorphous substrate. That is, the substrate should exhibit neither demonstrable scattering effects associated with polycrystalline boundaries and dislocations nor the birefringence found in many single crystals, nor other spurious effects.
As a result of the foregoing difficulties, research attempts to form together the active and passive parts of the integrated optical circuit on a common substrate have not been notably successful. Evidently, new insights are needed to over-leap this combination of problems and achieve economical and effective large-scale integration of such optical waveguiding circuits.